HBO’s True Blood received an invigorating, early renewal notice last summer; a third season will come out in June. And on film 2009 witnessed a quick, hungry revisit from Twilight, among others vampire flicks. Just this month, Ethan Hawke revealed himself in Daybreakers as Hollywood’s first hematologist-protagonist.

So it seems that now’s the perfect time to talk about it –

Blood, always my favorite Aristotelian humor, comprises two elements – plasma (a hazy yellowish fluid) and cells. The plasma bathes the blood cells in a mixture of salts and proteins as they travel within the walls of blood vessels throughout the body (the circulation) and in the chambers of the heart. Plasma proteins include some hormones, enzymes, clotting factors and antibodies.

Let’s start with some basics on the cellular components of blood: white blood cells, red blood cells and platelets:

neutrophil as seen in a peripheral blood smear, Wikimedia Commons (WC)

White Blood Cells

White blood cells (WBCs), physically larger than the rest, serve as warriors against infection. These include a cast of various types, each with a distinct role in battling germs. The most familiar white cells in the “peripheral blood” – as doctors refer to fluid passing through arteries and veins – are neutrophils, lymphocytes and monocytes. Two other forms, eosinophils and basophils, emerge from the bone marrow and typically travel in lesser numbers.

scanning micrograph, red blood cells, WC, adapted NIH image

Red Blood Cells

Red blood cells (RBCs), the most abundant and usually uniform blood cells, carry and deliver oxygen throughout the body. Mature, circulating red cells are disc-like in shape, indented on each side, and lack nuclei. They’re loaded with hemoglobin, a complex, iron-laden molecule that binds oxygen and turns blood red.

When someone receives a transfusion, that’s usually a unit of packed red blood cells, concentrated red cells from which most of the donor’s white cells, platelets and plasma have been removed.

Platelets

Platelets are tiny, blood clotting cells. Like red cells, these cells circulate without nuclei, but they’re irregular in shape and sticky, loaded inside with plug-forming proteins and on their surfaces with adhesive receptors, ready to clump at the nick of a chin or a pinprick.

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Both cancer and its treatments can affect the bone marrow, where blood cells are formed. Some tumors, like leukemia and lymphoma, arise from blood cells. Other medical conditions cause blood cell problems, too. For example, chronic kidney disease causes anemia, and HIV infection leads to reduced T-lymphocyte counts.

For all these reasons, I think it’s helpful for everyone to have some understanding of blood and blood cells – any discussion of stem cells, bone marrow and transplantation presupposes some knowledge of these basics.

More to follow!

Meanwhile, if you’re searching for more blood info on the Web, I suggest these sites: